sexual reproduction and meiosis

asexual reproduction

single individual passes on all of its genes to its progeny

sexual reproduction

Two parents give rise to progeny

the cell cycle

The process by which cells replicate their chromosomes and separate them into two new cells

G1 phase

gap (growth) phase, normal cellular function           

S phase

synthesis (DNA replication)

G2 phase

gap (growth) phase, preparation for M

Mitosis/M phase

division of the nucleus, then cytokinesis

G0 phase

cell cycle exit (arrest), cells go about normal function without dividing

Homologous chromosomes

1 maternal, 1 paternal

Monad

one DNA molecule/chromosome

Dyad

two sister chromatids, 2 dna molecules

sister chromatids

one chromosome, two copies of the same dna

meiosis

a form of cell division that produces the haploid gametes

gametes

sex cells (sperm and egg)

haploid

(n), 1 set of chromosomes, in humans = 23

diploid

(2n), 2 sets of chromosomes, one maternal and one paternal. In humans = 46 chromosomes

meiosis I

homologous chromosomes are separated into two new cells

meiosis II

sister chromatids are separated into 4 new cells

prophase I

chromosomes condense and nuclear envelope disintegrates

synapsis

homologous chromosomes pair with each other

bivalent/tetrad

pair of homologous chromosomes

crossing over

special part of meiosis where the maternal and paternal pairs swap DNA

chiasmata

structure formed by crossing over

metaphase I

homologous chromosomes line up on the metaphase plate and attach to meiotic spindle

cohesin

holds the sister chromatids together

anaphase I

homologous chromosomes are separated

separase

cleaves cohesin

shugoshin

protects the cohesins at the centromere during anaphase I

telophase I

cell divides to form 2 cells (23 chromosomes per cell, but 46 DNA molecules)

interkinesis

the period between meiosis I and meiosis II

prophase II

chromosomes condense and nuclear envelope disintegrates

metaphase II

individual chromosomes line up on equatorial plane

anaphase II

sister chromatids separate and are pulled to the poles

telophase II

cells divide to form 4 haploid (n) gametes

recombination

the process that causes crossing over

gametogenesis

production of haploid gametes

fertilization

fusion of the sperm and egg to form a diploid zygote

zygote

fusion of egg and sperm

spermatogenesis

production of sperm

spermatogonium

starting cell in spermatogenesis

spermatids

4 produced after spermatogenesis

oogenesis

production of eggs

oogonium

starting cell in oogenesis

ovum

1 produced after oogenesis

asexual advantages

saves energy, no courtship, greatest increase in fitness

asexual disadvantages

·      low genetic variability, adaptation to environment is difficult, slows evolution

sexual advantages

·      high genetic variability, facilitates adaptation, speeds up evolution

sexual disadvantages

energy costly, courtship is time and resource consuming, usually sacrifices the fitness of one sex to the other

two sources of genetic variation during meiosis

crossing over, the law of independent assortment